Alkali metal aluminosilicates, both crystalline (zeolites) and amorphous, are effective detergency builders which can be used to replace sodium tripolyphosphate (STP) in detergent powders, but they do not possess an ability comparable to that of STP to contribute to the structure of a spray-dried powder. Alkali metal silicates are frequently included in detergent powders as structurants, to reduce washing machine corrosion and to increase alkalinity. It is well known, however, that if aluminosilicate and silicate are together in a detergent slurry they can interact unfavourably: agglomeration of the aluminosilicate occurs to give powders containing large particles which are slow to disperse in the wash liquor, giving reduced washing performance.
EP 10 247B (Henkel KGaA) discloses a solution to this problem: silicate is omitted from the slurry, and instead is admixed subsequently with the spray-dried powder. The slurry contains aluminosilicate, surfactant and certain organic sequestrant builder materials, while the silicate is postdosed in the form of a powder having a Na.sub.2 O:SiO.sub.2 mole ratio of 2.0 to 2.2, a water content of 15-23% by weight and a high water solubility. Other ingredients unsuitable for spray-drying, for example, certain nonionic surfactants, may also be postdosed.
Powders made by this process exhibit improved washing performance, since the aluminosilicate is carried through into the powder, and into the wash, in the form of small particles. The physical properties of these powders tend, however, to be poor and the powder strength low.
We have now discovered that powders of greatly improved physical properties and attractive appearance may be produced by this method if there is included in the slurry an additional powder structurant which is a polymeric material.
Zeolite-built detergent powders containing anionic polymers are disclosed, for example, in EP 137 669A, EP 130 640A, EP 66 915A, EP 124 913A, and EP 63 399A (Procter & Gamble). Low or zero phosphate powders low in silicate and structured with water-soluble salts of succinic acid and anionic polymers are disclosed in our copending application No. 85 26999 filed on 1 Nov. 1985.
GB 2 095 274A (Colgate-Palmolive Co.) discloses in Example 2B spray-dried base beads containing zeolite, sodium bicarbonate, sodium carbonate, sodium nitrilotriacetate, bentonite clay and various minor ingredients including a small amount of sodium polyacrylate (0.1% based on the final product). The beads were oversprayed with nonionic surfactant, and 2.5% of hydrous sodium silicate of similar particle size and density were post-added. The level of sodium polyacrylate in this product, however, is too low for any structuring benefit to be obtained.